Searching for the cause of the acquired immune deficiency syndrome.

An outbreak of unexplained immune deficiency associated with opportunistic infection and Kaposi's sarcoma is occurring in the USA and other parts of the world. Affected individuals with what had come to be known as the acquired immune deficiency syndrome (AIDS) have a high mortality. Epidemiological features suggest the presence of a transmissable agent, but no responsible agent has yet been identified. Homosexual and bisexual men make up 75% of these affected individuals. Cytomegalovirus, Epstein Barr and herpes simplex viruses, organisms that commonly affect male homosexuals, may produce some features of AIDS. Individually or collectively, however, they can not account for the emergence of a previously unrecognized clinical syndrome. Hepatitis B is prevalent in patients with AIDS and may play a role as a co-factor in the disease. The properties of a number of other known viruses may provide a model for the pathogenesis of some features of the AIDS immunodeficiency. Newly described simian acquired immune deficiency syndrome (SAIDS) is the best available animal model. In man, the retrovirus, human T-cell leukemia virus (HTLV) may play a role in AIDS. However, HTLV or any other known virus cannot yet be assumed to cause AIDS. It is likely that an as yet unrecognized agent is the key causative agent of AIDS.